Crews remained on-scene late into the night Monday following a trench collapse that injured four workers at a construction site in Ajax.

The incident happened at around noon, on the roadway, near Rossland and Westney roads.

An Ornge air ambulance attended the scene and transported one person to hospital, Durham Regional Police told CTV News.

Ornge said their patient was a man in his 20s. He was taken to Toronto's Sunnybrook Health Sciences Centre with serious injuries, they said.

Another male victim was taken to a local hospital, Sgt. Joanna Bortoluss, of Durham Regional Police Service, told members of the media at the scene.

The extent of his injuries are unknown at this time.

Bortoluss said two other workers remain trapped in the trench.

A number of police, fire and rescue vehicles were still visible at the scene late Monday night, along with heavy equipment.   

Crews from Toronto Fire Services are also at the scene assisting emergency responders with the rescue operation.

Ontario's Ministry of Labour is on-scene as well and is investigating the incident.

Rossland Road remains closed between Ravenscroft and Westney roads.